Chapter 11 Part 3 Fundamentals of CNS

Chapter 11 Part 3 Fundamentals of CNS - Fundamentals of the...

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Unformatted text preview: Fundamentals of the Nervous System and Nervous Tissue Angela Peterson-Ford, PhD Part 3 apetersonford@collin.ed Nerve fibers are classified according to: Diameter Degree of myelination Speed of conduction Nerve Fiber Classification A junction that mediates information transfer from one neuron: To another neuron To an effector cell Presynaptic neuron conducts impulses toward the synapse Postsynaptic neuron transmits impulses away from the synapse Synapses Synapses Figure 11.17 Axodendritic synapses between the axon of one neuron and the dendrite of another Axosomatic synapses between the axon of one neuron and the soma of another Other types of synapses include: Axoaxonic (axon to axon) Dendrodendritic (dendrite to dendrite) Dendrosomatic (dendrites to soma) Types of Synapses Electrical synapses: Are less common than chemical synapses Correspond to gap junctions found in other cell types Are important in the CNS in: Arousal from sleep Mental attention Emotions and memory Ion and water homeostasis Electrical Synapses Electroencephalography (EEG) Specialized for the release and reception of neurotransmitters Typically composed of two parts: Axonal terminal of the presynaptic neuron, which contains synaptic vesicles Receptor region on the dendrite(s) or soma of the postsynaptic neuron Chemical Synapses Fluid-filled space separating the presynaptic and postsynaptic neurons Prevents nerve impulses from directly passing from one neuron to the next Transmission across the synaptic cleft: Is a chemical event (as opposed to an electrical one) Ensures unidirectional communication between neurons Synaptic Cleft Nerve impulses reach the axonal terminal of the presynaptic neuron and open Ca2+ channels Neurotransmitter is released into the synaptic cleft via exocytosis in response to synaptotagmin Neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic neuron Synaptic Cleft: Information Transfer Synaptic Cleft: Information Transfer Figure 11.19 Neurotransmitter bound to a postsynaptic neuron: Produces a continuous postsynaptic effect Blocks reception of additional messages Must be removed from its receptor Removal of neurotransmitters occurs when they: Are degraded by enzymes Are reabsorbed by astrocytes or the presynaptic terminals Diffuse from the synaptic cleft Termination of Neurotransmitter Effects Neurotransmitter must be released, diffuse across the synapse, and bind to receptors Synaptic delay time needed to do this (0.3-5.0 ms) Synaptic delay is the rate-limiting step of neural transmission Synaptic Delay...
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Chapter 11 Part 3 Fundamentals of CNS - Fundamentals of the...

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